function BackTop() {
    this.init();
}
BackTop.prototype = {
    constructor : BackTop,
    init : function() {
        this._initBackTop();
    },
    _initBackTop : function() {
        var $backTop = this.$backTop = $('<div class="cbbfixed">'
                + '<a class="cweixin cbbtn"">'
                + '<span class="weixin-icon"></span><div></div>' + '</a>'
                + '<a class="gotop cbbtn">' + '<span class="up-icon"></span>'
                + '</a>' + '</div>');
        $('body').append($backTop);

        $backTop.click(function() {
            $("html, body").animate({
                scrollTop : 0
            }, 120);
        });
        var timmer = null;
        $(window).bind("scroll",function() {
            var d = $(document).scrollTop(), e = $(window).height();
            0 < d ? $backTop.css("bottom", "10px") : $backTop.css(
                    "bottom", "-90px");
            clearTimeout(timmer);
            timmer = setTimeout(function() {
                clearTimeout(timmer)
            }, 100);
        });
    }

}
var BackTop = new BackTop();